Aim. Given the need to reduce the number of unnecessary laparoscopies, this study aimed to calculate the threshold values of contralateral testicular volume in unilateral non-palpable cryptorchidism to optimize diagnosis and surgical strategy.
Materials and methods. From 2010 to 2016, contralateral testicular volume was prospectively evaluated in 78 patients aged under nine years with unilateral non-palpable cryptorchidism. The volume of healthy testes was calculated by multiplying length * width * height * 0.71. The patients were divided into two groups. Group 1 comprised 41 (52.6%) children with inguinal or intra-abdominal testes, who underwent orchiopexy for undescended testis. The second group consisted of 37 (47.4%) patients with severely hypoplastic testes that needed to be removed, or with testicular aplasia. In both groups, we matched the age (in months) at the time of surgery and the volume of the contralateral testis. Logistic regression was used to develop the diagnostic model. For the model, the ROC-curve (Receiver Operating Characteristic) was constructed, and the threshold of the contralateral testicular volume was selected.
Results. All patients with contralateral testicular volume greater than 2.25 ml had testicular aplasia, or hypoplasia (sensitivity 100.0%, specificity 73.0%). All patients with a contralateral testicular volume less than or equal to 1.04 ml had inguinal or intra-abdominal testes (specificity of 100%, the sensitivity of 34%). The area under the ROC curve calculated to assess the quality of the model was 92.6%, suggesting the high predictive power of the model.
Conclusion. Revision scrototomy is indicated in patients with testicular volume exceeding 2.26 ml, while diagnostic laparoscopy is the optimal primary intervention in patients with the contralateral testicular volume of less than or equal to 1.04 ml.

Keywords: testicular volume, non-palpable testes, cryptorchidism, surgical treatment